Sam V. posted recently a bug report with a 64 bits kernel, running the pixma backend and a MF-4270 Canon MFP.
Details here: https://alioth.debian.org/tracker/?group_id=30186&atid=410366&func=detail&aid=310861 He has the pixma backend running fine with a 32 bits kernel (same version as 64 bits) in same conditions. On a 64 bits 2.6.25 kernel (Fedora 9) or 2.6.24 (Ubuntu), the logs show that sometimes (but not always, that's why scanning finally works, but takes very long time), there appears to be a: "Resource temporarily unavailable" error for read calls, from either sanei_usb_read_int() or sanei_usb_read_bulk(). They are triggered by usb_bulk_read() or usb_interrupt_read() calls from libusb. This error induces the timeouts, thus long scanning time. There do not appear to be errors on write calls (this would make scanning fail). I don't know what could cause this libusb error for the 64 bits kernel ? Anyone here already experienced this, or would have a clue ? Nicolas